In recent years, with the advancement of technologies for manufacturing projection devices, lightweight and slim projection devices have become the mainstream product in the market. The demands on new and improved products in the market have led to the continuous improvement of the design of projection devices. Accordingly, manufacturers of projection devices continuously develop small projection devices with a high efficiency and better imaging quality in order to satisfy the needs in the market.
Consequently, laser-phosphor based projectors were proposed to meet this requirement. FIG. 1A schematically illustrates the architecture of a conventional illumination system used in a single-chip digital light processing projector (DLP projector). FIG. 1B schematically illustrates a phosphor wheel of the illumination system of FIG. 1A. As shown in FIGS. 1A and 1B, the conventional illumination system 10 comprises a laser source 11, a lens group 12, and a phosphor wheel 13. The phosphor wheel 13 comprises plural segments 132 containing different phosphor agents 131. A laser light from the laser source 11 is transmitted through the lens group 12 and incident to the phosphor wheel 13 in order to excite a corresponding phosphor agent 131 of the phosphor wheel 13. Consequently, a color light with a longer wavelength (e.g. a red light) is produced. Upon rotation of the phosphor wheel 13, the plural segments 132 and the corresponding phosphor agents 131 of the phosphor wheel 13 are sequentially irradiated by the incident light. Consequently, various color lights (e.g. a red light, a green light, a yellow light and a blue light) are sequentially produced.
However, the conventional illumination system cannot be applied to a reflection-type phosphor wheel. Moreover, it is problematic to use color filters and phosphor agents on the phosphor wheel collaboratively. For example, the color lights outputted from the phosphor agents are scattered in all directions. According to the specifications, the incident angles relative to the color filters must be within a limited value in order to achieve good filtering performance.
From the above discussions, the conventional illumination system has complicated structures and fails to be applied to the reflection-type phosphor wheel. Moreover, the uses of the color filters cannot achieve good filtering performance. Since the wavelength conversion efficiency is impaired, the image quality is adversely affected.
Therefore, there is a need of providing an improved illumination system and a projection device with the illumination system in order to overcome the above drawbacks.